No font size? Interesting.
Debugging this will be a tedious process.
Because I soooo hate fiddle I created a working drag/drop of a textarea on codepen.
(BTW, this exact code wouldn’t work on fiddle but works fine on codepen.)
Go play around with it (you may have to shorten the dark working area to be able to actually play with the drag and drop.
After you’ve played around a bit, change the attributes of my textarea to the attributes of your AppStudio project textarea, run it again and make sure it works.